Hitherto, the composition of soft resin products applied, for example, to automobile internal trim parts comprises of in general polypropylene (hereinafter, referred to as "PP") from the standpoint of lightening the resin main body, the soft resin covering part thereof being formed with soft vinyl chloride (hereinafter, referred to as "soft PVC") or foamed soft PVC-polyurethane.
In the soft resin products of the above mentioned composition, there are found problems as mentioned hereinafter:
Now, there are explained for resin products which are obtained by a prior art:
(1) In FIG. 1-3, an example of resin product, i.e., a center cluster, is shown, in which a resin main body (resin insert) 1 of polypropylene (PP) is bonded to a soft resin covering part 2 formed from soft polyvinyl chloride (soft PVC) or foamed soft PVC-polyurethane by means of an adhesive 5 and then a paint 4 is coated on the surface of soft resin covering part 2. Because in the resin product, i.e., center cluster, the adhesion between the resin main body and the soft resin covering part is not so good that a layer of adhesive may be required, productivity of the resin product becomes low.
(2) As shown in FIG. 2--2, a resin product applied for automobile internal trim parts, i.e., center pillar, comprises of a resin main body (resin insert) 21 and a soft resin covering part 22, which is covered on the surface of the main body. As the resin main body 21, polyolefins are used from the viewpoint of lightening, and as the soft resin covering part 22, soft resins such as soft polyvinyl chloride and the like or foamed resins such as foamed polyvinyl chloride resin or foamed polyurethane resin are used. A decorating part 26 is then formed on the surface of the soft resin covering part 22 to use as automobile internal trim parts. However, when a soft polyvinyl chloride resin is used as the soft resin covering part 22 of such resin product as formed as above, there is a problem where the adhesion between the resin main body 21 and the covering part 22 is not good.
(3) Among resin products (i.e., kneepads) applied to an automobile, as shown in FIGS. 3-2 and 3-3, there is mentioned a resin product 34 which comprises a resin main body 31, a soft resin covering part 32 covered on the surface of the main body and a surface layer 33 formed thereon. In the resin product 34, from the viewpoint of lightening, polyolefin is generally used as the resin main body 31 and as said soft resin covering part 32, a foamed resin such as polyurethane and the like is used. And for the improvement of surface properties (for example, weather resistance, scratch resistance of exposed surface, etc.), a surface layer 33 of polyvinyl chloride resin is formed on the covering part 32. However, in the resin product 34, it is necessary for the thickness of the soft resin covering part 32 to be 4 mm or more in order to show the function of a foamed resin. Therefore, it is undesirable to form a resin product 34, in which the thickness of the covering part 32 is less than 4 mm, resulting in a restricted variation of shape design.
(4) As shown in FIGS. 4-2 and 4-3, a resin product 45 (i.e., a kneepad) in which a soft resin covering part 42 comprising a polyvinyl chloride resin foam or a polyurethane resin foam and the like is formed on a substrate 44 of metal plate and then a surface layer 43 of polyvinyl chloride and the like is laminated thereon to protect the covering part 42 is hitherto used. The resin product 45 of above-described structure is available in various kinds of fields, particularly in the field of automobile internal trim parts, and however, the softness of the resin product 45 is not shown sufficiently when the covering part 42 has not a thickness of more than a prescribed value, for example, more than 4 mm. Therefore, a resin product 45 of foam type can not be used for the application of small thickness resulting in a restricted variation of shape design. Moreover, in the process for the production of the resin product 45, the formation of foamed covering part 42 by pouring a foaming resin between a substrate 44 and a surface layer 43 requires a curing step which occupies much time, and further the removal of burrs after molding is necessary. Thus, there are problems in the process for the production of the resin product.
(5) A resin product 55 (i.e., kneepad), as shown in FIGS. 5-2 and 5-3, in which a soft resin coat part 52 comprising a polyvinyl chloride resin foam or a polyurethane resin foam is formed on a substrate 54 of metal plate and the covering part 52 is coated with a surface layer 53 of polyvinyl chloride resin and the like to protect the covering part is hitherto used. The resin product 55 of abovedescribed structure is available in various kinds of fields, particularly in the field of automobile internal trim parts and, however, the softness of the resin product 55 is not shown sufficiently when the covering part 52 has not a thickness of more than a prescribed value, for example, 4 mm or more. Therefore, there are problems where its use is restricted for the application of small thickness and for the variation of shape design. Moreover, in the process for the production of the resin product 55, the formation of foamed covering part 52 by pouring a foaming resin between a substrate 54 and a surface layer 53 requires a curing step which occupies much time and further the removal of burrs after molding is necessary. Thus, there are problems in the process for the production of the resin product.
(6) There are resin product having a general structure, in which a soft resin covering part (soft resin sheet) of soft resin is applied onto the surface of a resin main body of hard resin. As the soft resin covering part (soft resin sheet), there has been hitherto used widely a laminate sheet in which a thin resin main body (protective layer) of a polyvinyl chloride resin and the like is bonded to the surface of spongy soft resin covering part of foamed polyolefin resin and the like. For the formation of the resin product by using the laminate sheet, the following methods are employed:
(i) A laminate sheet is set previously on a metal mold for injection, a hard resin is then injection-molded onto the back surface of the laminate sheet to form a resin main body and at the same time bond the resin main body to the laminate sheet; PA1 (ii) A laminate sheet is set on a metal mold for blow-molding and a hard resin is blow-molded onto the back surface of the laminate sheet; and PA1 (iii) A stamping molding method. PA1 (a) The adhesion between the resin main body and the soft resin covering part is not good, so that it is necessary to activate the surface of the resin main body and apply adhesives thereon, resulting in a low productivity; PA1 (b) When a foamed resin such as a foamed polyvinyl chloride or a foamed polyurethane resin and the like which is used previously as said soft resin covering part, is used, it is necessary to keep the thickness of the soft resin covering part 4 mm or more to sufficiently show the function of the foam resin, resulting in a restricted variation of shape design of moldings.
However, there are problems where the adhesion between the spongy soft resin covering part and the resin main body in the laminate sheet is not good, and the spongy resin covering part having a thickness of less than 4 mm does not provide a soft touch.
Further, in the formation of the resin product with the laminate sheet by means of anyone of the methods (i) to (iii), there are found the following problems:
A laminate sheet is heated near to or above the softening temperature by means of molten hard resin for the resin main body or the metal mold in the molding process and subjected to a high molding pressure.
Accordingly, air foams (hereinafter, referred to as "voids") in the spongy covering part of laminate sheet are broken by the molding pressure resulting in that the resin product after molding does not show a sufficient soft feeling (touch).
Therefore, problems in soft resin products having the above-described structure are described as follows: